經常性的扭傷會導致踝關節的功能性不穩定(functional instability, FI)，而降低本體感覺敏感性與身體姿勢控制能力，研究證實踝關節扭傷可能會傷害踝關節週邊神經傳導或是神經傳送途徑，然而沒有任何研究探討FI徵兆對神經興奮性的可能影響。因此本研究目的為探討FI與健康踝關節本體感覺與Hoffmann反射的差異。21位受試者（9位雙踝健康，3位有單側FI徵兆，9位雙踝皆有FI徵兆）自願參與本研究，本體感覺是以Biodex Ⅲ等速肌力測試系統量測腳踝關節主動與被動復位誤差角度；而Hoffmann反射是以Dantec Keypoint®來量測下肢比目魚肌的最大H-reflex與M wave，所得實驗數據以獨立樣本t檢定與Pearson相關係數統計分析其間的差異與關係，統計顯著水準定為p<.05。結果顯示FI踝關節較健康踝關節有顯著較大的絕對復位誤差角度(ARS 3.48 ± 1.45° vs. 2.18 ± 0.69°; PRS 3.68 ± 1.45° vs. 2.31 ± 0.83°)與顯著較小的H-reflex最大振幅(4.32 ± 2.93 mV vs. 6.12 ± 2.59 mV)。本研究驗證FI踝關節會有顯著較差的本體感覺與較低的運動神經興奮性，降低的本體感覺功能可能與踝損傷後壓力感受訊號傳入受損有關，而較低的Hoffmann反射振幅可能與傳入終點減少的神經傳導物質有關。

Repeated ankle sprains would result in functional instability (FI), and decrease the proprioception sensitivity and the postural control ability. It also demonstrated that ankle sprain might impair the nerve conduction or neuron pathway surrounding the ankle joint. However, no study has investigated the influences of FI on motoneuron excitability. The purpose of this study compared the difference in proprioception and the Hoffmann reflexes between FI and normal health (NH) ankles. Twenty-one subjects (9 healthy, 3 unilateral FI, and 9 bilateral FI) were recruited. The proprioception was measured by the Biodex Ⅲ dynamometer as ankle active/passive reposition sense. The soleus Hoffmann reflex was measured by Dantec Keypoint as H-reflex and M wave maximal amplitude. An independent ttest and a Pearson correlation analysis were used to examine the difference and relationship between FI and NH ankles. The statistic significance was set at p<.05. The results of this study showed that FI ankle had a greater absolute reposition error angle but smaller H-reflex maximal amplitudes than the general population. This study demonstrated that the FI ankle had a significantly poor proprioception and a lower motoneuron excitability. It is suggested that the decreased sensitivity of ankle proprioception might be due to the impaired mechanoreceptors in the functional instability ankle. In addition, the lowered maximal amplitude of the Hoffmann reflex might be due to the diminished numbers of the neurotransmitter released by the afferent terminal.